What exactly were you thinking about doing? A window sticker? Or incorporating a tail stripe? Single color or multiple colors? Maybe something centered on the trunk lid?
If I could make a suggestion... - I would try to modify the emblems used during that time period (1940). That way they would have a more significant connection with the car. I looked for some images on Google to get an idea of possible directions to start with.
If you get a chance try to send me more pics of the coupe so I can get a better idea of options for you to consider.
Mr Norm had produced a Dodge Rumbler that has an insignia very close to what you might want. It could easily be modified to blend with your '40.
You could personalize the lettering. This would be a rough example.